ARTICLE pubs.acs.org/crystal
Supramolecular Hexagon and Chain Coordination Polymer Containing the MoO22þ Core: Structural Transformation in the Solid State alogovic,§ Jana Pisk,§ Renata Dreos,‡ and Visnja Vrdoljak,*,§ Biserka Prugovecki,§ Dubravka Matkovic-C ‡ Patrizia Siega § ‡
Department of Chemistry, Faculty of Science, University of Zagreb, Horvatovac 102a, 10000 Zagreb, Croatia Department of Chemistry, University of Trieste, Via L. Giorgieri 1, 34127, Trieste, Italy
bS Supporting Information ABSTRACT: The reaction of [MoO2(acac)2] (where acac = acetylacetonate ligand) with the salicylaldehyde isonicotinyl hydrazonate ligand (SIH2-) yielded a zigzag chain polymer [MoO2(SIH)]n (1), an interwoven hexagon [MoO2(SIH)]6 (2), or the mononuclear complexes [MoO2(SIH)(C2H5OH)] (3EtOH) and [MoO2(SIH)(C3H7OH)] (3PrOH). Diversity in the formation of dioxomolybdenum(VI) compounds illustrates their sensitivity to the reaction conditions. Crystal and molecular structures of all of the investigated molybdenum(VI) compounds were determined by the single crystal X-ray diffraction method. Solid-state reactions lead to the transformation of the supramolecular hexagon or the mononuclear complexes into the chain coordination polymer. These thermally induced conversions were characterized by the X-ray powder diffraction method. All of the investigated compounds were further characterized by elemental analysis, thermogravimetric analyses, Fourier transform infrared (FT-IR), and NMR spectroscopy.
’ INTRODUCTION An important part of supramolecular chemistry refers to the coordination driven self-assembled structures. Such supramolecular architectures exhibit a wide variety of properties, for example, redox,1 magnetic,2 catalytic,3 or optical,4 and therefore represent attractive materials in connection with numerous possible applications.5 They can in principle be generated by self-assembly of a wide range of suitable building blocks in solution as well as in the solid state.6 In this context, metal complexes with coordinatively unsaturated metal ions or those with easily available coordination sites are of special interest.7 Otherwise, they can be constructed through supramolecule-tosupramolecule transformation.8,9 Generally, reactions and structural conversions in the solid state are more difficult than in solution since they involve cleavage and/or formation of new bonds with limited movements of molecules.6b Furthermore, intrasolid topochemical conversions are expected to occur only between molecules that are suitably arranged, with reacting centers close to each other within the crystal.10,11 Therefore, investigation of photochemically12 or thermally13 induced solidstate reactions are continuing to be a challenging area of supramolecular chemistry. A wide variety of compounds having either discrete, polyhedral, or infinite structures can be generated depending on the chosen strategy.14 Although supramolecular squares, zigzag chains, or helical chains are generally achieved by combining r 2011 American Chemical Society
octahedral metal complexes with organic ligand linkers,4,15 supramolecular hexagons possessing 90° angular building units are also possible.16 They represent discrete non-coplanar species (interwoven or parallel) of which only a few have been reported. On the other hand, hexanuclear metallacycles which have approximately planar ring structures are more numerous but still relatively scarce.17 They are usually constructed by combining complementary 120° and 180° angular building blocks. Pentacoordinated dioxomolybdenum complexes have a great tendency to form polymeric18 or dimeric compounds,19 in which metal centers are connected through bridging oxygen atoms, in the course of the ModO 3 3 3 ModO interaction. For that reason, construction of supramolecular architectures with cisdioxomolybdenum(VI) building blocks is very difficult to realize. Recently, we have published the first example of zigzag and square compounds containing the cis-MoO22þ core with the linker group being the isonicotinyl part of the aroylhydrazone ligands.20 To expand the knowledge in this field we investigated: (a) possible supramolecular isomerism; (b) supramolecule-to-supramolecule transformation; (c) structural conversion in the Received: November 3, 2010 Revised: January 14, 2011 Published: February 08, 2011 1244
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Table 1. Crystallographic Data for Compounds 1, 2, 3EtOH, and 3PrOH 1
2
3EtOH
3PrOH
chemical formula
C13H9MoN3O4
C78H54Mo6N18O24
C15H15MoN3O5
C16H17MoN3O5
Mr
367.17
2203.03
413.24
427.27
crystal color, habit
orange, plate
orange, plate
orange, plate
orange, plate
crystal size (mm3)
0.41, 0.35, 0.06
0.54, 0.34, 0.08
0.58, 0.28, 0.04
0.62, 0.34, 0.02
crystal system
monoclinic
trigonal
monoclinic
monoclinic
space group
P21/n
R3
P21/n
P21/n
10.3077(12) 12.4577(10)
35.8324(7) 35.8324(7)
8.1976(2) 12.4876(2)
8.0154(10) 13.662(2)
unit cell parameters a (Å) b (Å) c (Å)
11.7642(12)
6.5470(2)
15.4540(3)
15.4013(10)
R (°)
90
90
90
90
β (°)
112.060(12)
90
96.841(2)
98.980(8)
γ (°)
90
120
90
90
V (Å3)
1400.1(2)
7279.9(3)
1570.74(6)
1665.9(3)
Z
4
3
4
4
Dcalc (g cm-3) temperature (K)
1.729 120
1.508 120
1.747 120
1.704 120
μ (mm-1)
0.955
0.827
0.867
0.820
F(000)
728
3276
832
864
number of unique data
3008
2802
2755
2920
number of data [Fo g 4σ(Fo)]
2442
2229
2561
2454
number of parameters
190
190
221
230
R1a, [Fo g 4σ(Fo)]
0.0287
0.0343
0.0181
0.0285
wR2b goodness of fit on F2, Sc
0.0763 1.06
0.0982 1.00
0.0493 1.09
0.0770 1.03
-0.46, 1.04d
-0.39, 0.26
-0.46, 0.64
min and max electron density (e Å-3) a
-0.41, 0.46
R = Σ||Fo| - |Fc||/Σ|Fo|. wR = Σ(Fo - Fc ) /Σw(Fo ) ] b
2
2 2
. S = Σ[w(Fo2 - Fc2)2/(Nobs - Nparam)]1/2. d The maximum density is 3.53 Å from O3.
2 2 1/2 c
solid-state; (d) ability of the architectures to modify by changing the medium. To achieve this aim, we have chosen the [MoO2(SIH)] building unit, involving the salicylaldehyde isonicotinylhydrazoate ligand (SIH2-, Scheme S1, Supporting Information), to exclude the possibility of steric hindrance or influence of the substituents (electron donating or withdrawing) on the formation of the superstructures. Reported structurally characterized metal complexes with the SIH2- ligand are usually mononuclear.21 Only one dimeric manganese(III) complex22 and one two-dimensional (2-D) lead(II) polymer23 have been reported so far.
’ EXPERIMENTAL SECTION Physical Methods. Infrared spectra were recorded in KBr pellets with a Perkin-Elmer 502 spectrophotometer in the 4500-450 cm-1 region. Elemental analyses were provided by the Analytical Services Laboratory of the Ru{er Boskovic Institute, Zagreb. Thermogravimetric (TG) analyses were performed using Mettler TG 50 thermobalance with aluminum crucibles. Differential scanning calorimetry (DSC) measurements were undertaken using a Mettler-Toledo DSC823e calorimeter. The results were developed by applying the Mettler STARe 9.01 software. All experiments were recorded in a dynamic atmosphere with a flow rate of 200 cm3 min-1. 1H, 13C, COSY and ROESY spectra were obtained using a Jeol EX-400 instrument (1H at 400 MHz and 13C at 100.4 MHz) and Jeol EX-270. Edited 1H-13C gHSQCAD and 1H-15N gHMBCAD spectra were recorded on a Varian 500 Inova instrument (1H at 499 MHz, 13C at 125.7 MHz and 15N at 50.7 MHz).
X-ray Crystallography. Single Crystal Diffraction. The single-crystal X-ray diffraction data of 1, 2, 3EtOH, and 3PrOH were collected by ω-scans on an Oxford Diffraction Xcalibur 3 CCD diffractometer with graphite-monochromated Mo-KR radiation (λ = 0.71073 Å). The data reduction was performed using the CrysAlis software package.24 Solution, refinement, and analysis of the structures were done using the programs integrated in the WinGX system.25 The structures were solved using SHELXS26 by the Patterson method. The refinement procedure was performed by the full-matrix least-squares method based on F2 against all reflections using SHELXL-97.27 The non-hydrogen atoms were refined anisotropically. All hydrogen atoms were located in the difference Fourier maps. Because of poor geometry for some of them, they were placed in calculated positions and refined using the riding model. Only the hydrogen atoms on the alcohol molecules were refined. Geometrical calculations were done using PLATON.28,29 The structure drawings were prepared using PLATON and MERCURY30 programs. The crystallographic data are summarized in Table 1, whereas the selected bond distances and angles are listed in Table S1, Supporting Information. In order to resolve the low electron density in the voids of 2 found in the final difference Fourier map, three additional diffraction data sets were collected from different crystals under different conditions (a quick data collection at 120 K; data collection at room temperature and data collection at room temperature after heating of 2 to 413 K when the crystals were no longer transparent; Table S2, Supporting Information). Powder Diffraction. The powder X-ray diffraction data were collected by the Panalytical X’Change powder diffractometer in the BraggBrentano geometry using CuKR radiation. The sample was contained on a Si sample holder. The patterns were collected in the range of 1245
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Crystal Growth & Design 2θ = 5°-50° with the step size of 0.03° and at 1.5 s per step. The data were collected and visualized using the X’Pert programs Suite.31 Preparative Part. The starting complex [MoO2(acac)2] (where acac = acetylacetonate ligand) was prepared as described in the literature.32 Salicylaldehyde, isonicotinyl hydrazine, benzonitrile, and alcohols were commercially available. Alcohols were dried using magnesium turnings and iodine and then distilled. Salicylaldehyde isonicotinyl hydrazone (H2SIH) and [MoO2(SIH)(CH3OH)] (3MeOH in the Supporting Information) were prepared according to the procedures described in the literature.33 All compounds were characterized by IR and NMR spectroscopy, thermal and elemental analyses (data are given in the Supporting Information). [MoO2(SIH)]n (1). A mixture of [MoO2(acac)2] (0.1 g, 0.30 mmol) and H2SIH (0.07 g, 0.30 mmol) in isopropanol (20 mL) was heated at 40-50 °C for 4 h. The obtained precipitate was filtered, rinsed with isopropanol, and dried in a desiccator up to the constant weight. An orange product was obtained. Yield: 0.07 g; 62%. The product can also be obtained by the solid-state transformation of [MoO2(SIH)]6 (2) or [MoO2(SIH)(ROH)] (3) (R = CH3, C2H5, or C3H7). [MoO2(SIH)]6 (2). A mixture of [MoO2(acac)2] (0.05 g, 0.15 mmol) and H2SIH (0.03 g, 0.1 mmol) in benzonitrile (10 mL) was heated at 100 °C for 4 h. The solution was left at room temperature for 2-3 days and the obtained precipitate was filtered, rinsed with tetrachloromethane, and dried in a desiccator up to the constant weight. An orange product was obtained. Yield: 0.03 g; 53%. [MoO2(SIH)(ROH)] (3ROH). A mixture of [MoO2(acac)2] (0.1 g, 0.30 mmol) and H2SIH (0.09 g, 0.30 mmol) in an appropriate alcohol (50 mL) was heated at 40-50 °C for 4 h. The solution was left at room temperature for a few days. The obtained orange precipitate was filtered, rinsed with the same alcohol, and dried in a desiccator up to the constant weight. [MoO2(SIH)(C2H5OH)] (3EtOH): Yield: 0.10 g; 79%. [MoO2(SIH)(C3H7OH)] (3PrOH): Yield: 0.09 g; 68%.
’ RESULTS AND DISCUSSION Preparation. Replacement of two acetylacetonate ligands in [MoO2(acac)2] by salicylaldehyde isonicotinyl hydrazonate (SIH2-) resulted in the formation of a zigzag chain polymer [MoO2(SIH)]n (1), interwoven hexagon [MoO2(SIH)]6 (2), or mononuclear complexes [MoO2(SIH)(C2H5OH)] (3EtOH) and [MoO2(SIH)(C3H7OH)] (3PrOH) (Scheme 1). In all of these compounds the dinegative ligand is coordinated to the cisMoO22þ core via the phenolic-oxygen, azomethine-nitrogen, and enolic-oxygen. The ligand possesses a fourth donor site, the nitrogen atom of the isonicotinyl part, that coordinates the remaining sixth coordination site of a neighboring dioxomolybdenum(VI) center, thereby producing 1 or 2. To the best of our knowledge, self-assembly of octahedral cis-dioxomolybdenum(VI) into a molecular hexagon has not been reported so far. Otherwise, the sixth coordination site is occupied by the oxygen atom from the solvent thus forming the mononuclear complexes (3EtOH or 3PrOH). Despite the possibility of construction of several products, we have established procedures for the selective formation of each compound by changing conditions such as the concentration, temperature, or the reaction medium. The formation of polymer 1, hexagon 2, or/and mononuclear complexes 3EtOH and 3PrOH in an appropriate alcohol ROH (R = C2H5 or C3H7) depends on the donor strength of the solvent. Thus, the reaction in methanol resulted only in the mononuclear compound [MoO2(SIH)(CH3OH)] (3MeOH), and no evidence for any supramolecular assembly was found (as proven by X-ray powder diffraction, Figure S1, Supporting
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Scheme 1. Synthesis of Compounds 1, 2, and 3ROHa
a
The reactions depicted by blue arrows were performed in dry solvents, while those depicted by red arrows were done in the solid state.
Information). The crystals of 3MeOH are identical to those known from the literature.21b The reaction in ethanol resulted in the formation of 1 and 3EtOH, whereas the complexation of cisMoO22þ with SIH2- in isopropanol yielded 1, 2, or 3PrOH. Polymer 1 can be prepared as the only product (either from ethanol or isopropanol) by increasing the concentration of the solution (Figure S2, Supporting Information), while pure mononuclear compounds 3EtOH and 3PrOH dominate in very dilute solutions (Figure S1, Supporting Information). By decreasing the concentrations of the starting agents in the isopropanolic solution, the reaction first gives rise to a hexagon-polymer mixture. The proportion of 2 increased with respect to that of 1 at lower concentrations, and vice versa. Since formation of the hexagon was possible only in the solvent that is the weakest donor among the used alcohols, the reactions were performed using even weaker donor solvents, acetonitrile and benzonitrile. The self-assembly of the complex in an acetonitrile solution again yielded a mixture of isomers 1 and 2, regardless of the concentration or temperature of the reaction mixture. Finally, hexamer 2 is generated preferentially in benzonitrile at 100 °C (Figure S3, Supporting Information). By dissolving 1 or 2 in the appropriate alcohol ROH, the supramolecular architectures can be transformed into monomeric [MoO2(SIH)(ROH)] (Scheme 1). This suggests that the nitrogen atom of the isonicotinyl part can easily be replaced by the alcohol molecule in the coordination sphere of molybdenum. Monomerization can more easily be achieved by addition of a stronger coordinating ligand, such as DMF, or DMSO (compound 3DMSO in the Supporting Information). However, solubility problems of [MoO2 (SIH)(ROH)] in benzonitrile prevented attempts to convert them back into 2. Thermal Analysis and Structural Transformations in the Solid State. All monomers [MoO2(SIH)(ROH)] show similar 1246
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Figure 1. Powder X-ray diffraction patterns of (a) 2 obtained upon reaction in benzonitrile; (b-f) samples obtained when 2 was heated from the ambient to various end temperatures at 10 °C min-1, and then heated isothermally for 1 h; (b) 190 °C, (c) 200 °C, (d) 210 °C, (e) 215 °C, and (f) 250 °C; (g) 1 obtained upon reaction in C3H7OH.
thermal behavior. The first weight loss in the thermogravimetric curves was related to the loss of the coordinated ROH molecule. In the atmosphere of pure oxygen (at a heating rate of 5 °C min-1), weight losses of a finely ground sample occurred in the range 158181 °C (CH3OH); 134-180 °C (C2H5OH) and 120-142 °C (C3H7OH). Afterward, an intermediate product is stable up to 353 °C, which then starts to decompose and finally affords MoO3 (at ca. 485 °C). We were interested in the possibility of thermally induced structural transformation of 3MeOH, 3EtOH, and 3PrOH in solvent-free conditions. Therefore, crystalline samples of each of the [MoO2(SIH)(ROH)] compounds were heated from the ambient temperature up to 250 °C (with a heating rate of 10 °C min-1) and then isothermally for 1 h. This process resulted in an endothermic peak in the DSC curve (70.7 kJ mol-1 (3MeOH, Figure S4, Supporting Information); 63.3 kJ mol-1 (3EtOH) and 63.2 kJ mol-1 (3PrOH)). The monomers, after losing ROH, interlinked to give the zigzag polymer [MoO2(SIH)]n (1), Scheme 1, which was identified by X-ray powder diffraction (Figure S5, Supporting Information). DSC measurements suggest that the loss of the coordinated ROH molecule is simultaneously accompanied by coordination of the nitrogen atom of the isonicotinyl part to molybdenum since no peaks were observed in the temperature range after losing ROH. The transformation could be explained by the movement of neighboring molecules, which are orientated favorably (Figure S6, Supporting Information). Formation of a supramolecular architecture by the solid-state polymerization of mononuclear dioxomolybdenum(VI) complexes has not been reported so far. Thermogravimetric analysis of hexagon 2 (Figure S7, Supporting Information) reveals its high thermal stability (at about 350 °C the substance decomposes). To examine more profoundly the properties of hexagon 2, a crystalline sample was heated from ambient to various end temperatures, and then isothermally for 1 h. When the sample of 2 was heated up to 190 °C the resulting crystals of 2a showed lower transparency in comparison with that of the original material (Figure S8,
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Supporting Information). However, the same crystal structure as that of 2 was confirmed by the single crystal X-ray diffraction method (Table S2, Supporting Information). Further increase of the temperature resulted in cracking of the crystals. Comparison of the X-ray powder diffraction patterns of the resulting material with those of 1 and 2 demonstrates that the material at 215 °C is exclusively that of 1 (Figure 1). The supramolecule to supramolecule transformation can be explained by the cleavage of the Mo-N(isonicotinyl) bonds in the hexagon and formation of new Mo-N(isonicotinyl) bonds. Up to now, the structural transformation of discrete self-assembled supramolecules based upon the MoO22þ core by a solvent free-reaction has not been reported. Spectroscopic Characterization. Absence of the bands characteristic of the N-H and CdO groups (at 3180 and 1685 cm-1, respectively) indicates enolization of H2SIH and coordination through the deprotonated enolic-oxygen atom. Appearance of a new band at 1342 cm-1 (1 or 2) and at 1362 cm-1 (3MeOH, 3EtOH, and 3PrOH) also proves enolization. The absorption bands belonging to CdNimine and C-Ophenolic groups (at 1601 cm-1 and 1566 cm-1, respectively) seen in the IR spectrum of H2SIH are shifted to ca. 1600 cm-1 and 1553 cm-1 in the spectra of all of the complexes.34 This indicates coordination of SIH2- to the cis-MoO22þ core via the phenolic-oxygen and azomethine-nitrogen. Compounds 1 and 2 exhibit the CdNisonicotinyl stretching frequency shifted by ca. 20 cm-1 in comparison with the IR spectra of [MoO2SIH(ROH)], which clearly indicates formation of the Mo-N(isonicotinyl) bond and not an intermolecular ModO 3 3 3 Mo interaction.35 This was additionally supported by the absence of a strong band at ∼850 cm-1, which is characteristic for a molybdenum 3 3 3 oxygen interaction.18,19 Appearance of a new band at ∼1050 cm-1 in the IR spectra of the mononuclear complexes confirmed coordination of the ROH molecule to the molybdenum atom in compounds [MoO2SIH(ROH)].33b For all complexes, the stretching frequencies characteristic of the symmetric and asymmetric vibrations of the cis-MoO22þ structural unit are found at about 945-938 cm-1 and 917-911 cm-1, respectively.36 The ligand H2SIH, dissolved in DMSO-d6, gives rise to two sets of 1H NMR signals with an integrated intensity ratio of about 1:0.07. A ROESY experiment shows exchange cross-peaks between the signals of the high and low integrating sets. As recently reported for similar molecules,20 this result indicates that two isomers are present in the solution, with slow interconversion on the NMR time scale at 298 K. The chemical shift and the assignment of the signals of the higher set, performed through COSY, ROESY, 1H-13C gHSQCAD, and 1H-15N gHMBCAD experiments (in the Supporting Information), are in agreement with those already reported,33b except for the signals at 11.08 ppm (OH) and 12.31 ppm (NH), whose assignment, carried out by 1 H-15N gHMBCAD experiment, has been reversed. NOE contacts between H-N2 and both azomethine H-CdN and pyridine meta protons, together with the through-H-bond scalar coupling between N1 and OH in the 1H-15N-gHMBCAD experiment, strongly suggest that the ligand adopts the E conformation with respect to the CdN bond, as depicted in Scheme S2, Supporting Information (amide group is trans). The low integrating set signals were assigned through the cited ROESY exchange cross peaks. The OH, NH, and H-CdN signals show an upfield shift (Δδ = -1.01, -0.27, and -0.35 ppm, respectively) with respect to the high integrating set. These data, together with the relatively high coalescence temperature (ca. 348 K), 1247
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Figure 2. Molecular drawing of [MoO2(SIH)]n (1): (a) ORTEP plot of the crystal structure of [MoO2(SIH)]n with displacement ellipsoids of nonhydrogen atoms drawn at the 30% probability level; (b) packing arrangement of the chains displayed in the unit cell. (c) The same packing in the spacefill style.
measured through variable temperature experiments, suggest that the conformation of the minor isomer is Z (Scheme S2, Supporting Information).37,20 For both isomers, correlation signals via 1J (N,H) are observed in the 1H-15N-gHMBCAD experiment for the NH groups, indicating that neither of the isomers are in the enolic form. The 1H NMR spectra of [MoO2(SIH)(EtOH)], [MoO2 (SIH)]n, and [MoO2(SIH)]6 in DMSO-d6 are superimposable, except for the presence of resonances attributed to free EtOH in the spectrum of the former, indicating a displacement of EtOH by DMSO-d6. The NH and OH signals of free H2SIH are not observed, and the azomethine CHdN signal is shifted downfield (Δδ = þ0.35 ppm). These results are in agreement with a doubledeprotonation of the ligand and its coordination to Mo through the phenolic oxygen and the O-atom arising from the enolization of N-CdO group, and also in agreement with the X-ray structures. The superimposability of 1H NMR spectra of [MoO2(SIH)]n, and [MoO2(SIH)]6 with that of [MoO2(SIH)(EtOH)] suggests that all these compounds are mononuclear [MoO2(SIH)(C2H6OS)]
(3DMSO in the Supporting Information) in the DMSO-d6 solution. NMR analysis in noncoordinating solvents was hindered by the very low solubility in these solvents. Crystal and Molecular Structures. Complex 1 consists of infinite one-dimensional zigzag chains running parallel to the b axis. The molybdenum atom exhibits a distorted octahedral coordination sphere comprised of two oxo-oxygen atoms, three donor atoms from the SIH2- ligand, and a nitrogen atom of the isonicotinyl moiety (Figure 2). The distance between molybdenum and nitrogen atom of the isonicotinyl moiety, Mo1-N3(-1/2 - x, 1/2 þ y, 1/2 - z) of 2.486(2) Å represents the largest bond length within the distorted octahedron (Table S1, Supporting Information). The ligand is not planar. The angle between the phenyl and the isonicotinyl moiety is 9.3(2)°, and the angle between the fiveand six-membered chelate ring is 8.71(10)°. There are no classical hydrogen bonds in the polymer crystal structure; however weak intermolecular hydrogen bonds are present (Table S3, 1248
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Figure 3. Molecular drawing of [MoO2(SIH)]6 (2): (a) ORTEP plot of the crystal structure of [MoO2(SIH)]6 displacement ellipsoids of nonhydrogen atoms are drawn at the 30% probability level; (b) packing arrangement of [MoO2(SIH)]6 molecules displayed in the unit cell; (c) the same packing in the spacefill style.
Supporting Information), C4-H4 3 3 3 N1[-1/2 - x, -1/2 þ y, 1/2 - z] 3.108(3) Å, C4-H4 3 3 3 O4[-x, -y, 1 - z] 3.170(3) Å, and C5-H5 3 3 3 O4[-1/2 - x, -1/2 þ y, 1/2 - z] 2.955(5) Å. The supramolecular interwoven hexagon 2 (Figure 3) is comprised of six units of [MoO2(SIH)], in which the molybdenum atoms exhibit distorted octahedral coordination spheres. The distance between the molybdenum and nitrogen atom of the isonicotinyl moiety Mo1-N3(-1/3 þ x -y, -1/3 þ x, 5/3 - z) of 2.431(3) Å represents the largest bond length within the distorted octahedron (Table S3, Supporting Information). The SIH2- ligand does not deviate as much from planarity as in 1: the angle between the phenyl and the isonicotinyl moiety is 7.6(2)°, and the five- and six-membered chelate rings form an angle of 6.1(1)°. The ring has a diameter of 13.28 Å based on the distance between centroids of two opposite pyridine rings in the hexagon. A view along the crystallographic c axis shows the molecular hexagons stacked
one upon the other, thus forming microporous hexagonal channels (Figure 3b, Figure S9 in the Supporting Information). There are no classical hydrogen bonds in the hexagon crystal structure, but there are weak hydrogen bonds of the C-H 3 3 3 O type (Table S3, Supporting Information). The volume of the solvent accessible area of each hexagon void in the unit cell of 2 is 545 Å (1635 Å within the whole unit cell, which amounts to 22.5% of the unit cell volume). The crystallographic data of all four data sets indicate several maxima of only small residual electron density within these channels. Interestingly, the density in all data sets was at approximately the same site (Table S2, Supporting Information). Even after a close inspection of the density with program COOT38 (Figure S10, Supporting Information), we were not able to identify its origin. Some authors suggest that such a small residual electron density in the hexagonal channels indicates that the channels are empty or might entrap trace amounts of solvent molecules.16c,17b However, TG and DSC measurements of 2 are consistent with 1249
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Figure 4. Molecular drawing of 3EtOH: (a) ORTEP plot of the crystal structure of 3EtOH displacement ellipsoids of non-hydrogen atoms are drawn at the 30% probability level; (b) packing arrangement of 3EtOH molecules displayed in the unit cell.
Figure 5. Molecular drawing of 3PrOH: (a) ORTEP plot of the crystal structure of 3PrOH displacement ellipsoids of non-hydrogen atoms are drawn at the 30% probability level; (b) packing arrangement of 3PrOH molecules displayed in the unit cell.
the absence of any significant amount of trapped solvent molecules. In 3EtOH and 3PrOH, the sixth coordination molybdenum site is occupied by the oxygen atom from the alcohol (ethanol in 3EtOH and isopropanol in 3PrOH) forming the mononuclear complex (Figures 4a and 5a). Molybdenum atoms exhibit distorted octahedral coordination spheres; the distance between the molybdenum atom and the oxygen atom of the alcohol molecule, Mo1-O5 of 2.3353(16) Å and 2.382(2) Å in 3EtOH and 3PrOH, respectively, represents the largest bond length within the distorted octahedron (Table S1, Supporting Information). The SIH2- ligand deviates more from planarity than in 1 and 2: the angle between the phenyl and the isonicotinyl moiety is 9.4(6)° and 7.71(9)°; the five- and six-membered chelate rings form an angle of 17.60(9)° and 22.53(13)° in 3EtOH and 3PrOH, respectively. In the crystal structure of 3EtOH and 3PrOH, there are pairs of centrosymmetrically related hydrogen bonds
O5-H1 3 3 3 N3[1 - x, 1 - y, -z] 2.730(2) Å and O5-H1 3 3 3 N3[1 - x, -y, 2 - z] 2.798(3) Å, connecting the molecules into dimers (Figures 4b and 5b, respectively). Weak C-H 3 3 3 O hydrogen bonds (C3-H3 3 3 3 O2[1/2 - x, 1/2 þ y, 1/2 - z] 3.380(2) Å are also present in 3EtOH and C3-H3 3 3 3 O2[3/2 - x, -1/2 þ y, 3/2 - z] 3.459(3) Å, C7-H7 3 3 3 O3 [1/2 - x, 1/2 - y, 1/2 þ z] 3.358(3) Å, C15-H15A 3 3 3 O4 [-1 þ x, y, z] 3.358(4) Å and C16H16B 3 3 3 O4[3/2 - x, 1/2 þ y, 3/2 - z] 3.178(3) Å in 3PrOH (Table S3 in the Supporting Information). The packing of molecules in the unit cell of 3MeOH, 3EtOH, and 3PrOH shows remarkable similarity (Figure S11, Supporting Information), as can also be seen from their similar unit cells (Table 1; a = 8.182(1), b = 12.472(2), c = 15.075(2) Å, β = 97.96(1)° in 3MeOH) and similar powder diffraction patterns (Figure S1, Supporting Information). The aliphatic part of the alcohol moiety takes part only in weak interactions that do not influence significantly the crystal packing. 1250
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Crystal Growth & Design The Mo-O and Mo-N bond lengths that are trans to the oxo-oxygen atom are lengthened in all of the investigated complexes due to the trans-influence (Table S1, Supporting Information). The C7-N1 bond in complexes 1, 2, 3EtOH, and 3PrOH varies from 1.284(2) to 1.292(3) Å and is not significantly different than in the free ligand 1.2756(16) Å.39 The bond length N2-C1 is shortened (in the complexes it is in the range from 1.279(6) to 1.300(3) Å, while in the ligand it amounts to 1.3558(17) Å), whereas that of N1-N2 is lengthened in the complexes (1.393(5)-1.399(6) Å) in comparison to the free ligand (1.3699(15) Å) due to the electron delocalization.
’ CONCLUSIONS Supramolecular assemblies [MoO2(SIH)]n (1) and [MoO2 (SIH)]6 (2) are generated by the 1:1 stoichiometric reaction between [MoO2(acac)2] with a SIH2- ligand. The formation of 1 and 2 can be controlled by the nature of the solvent as well as the medium concentration. Compound 1 consists of infinite zigzag chains held together only by weak hydrogen bonds. Compound 2 is comprised of interwoven hexagons stacked in an eclipsed manner, thus forming microporous channels stable up to 200 °C without losing framework integrity. There are no classical hydrogen bonds in the hexagon crystal structure, but there are weak hydrogen bonds of the C-H 3 3 3 O type. Thermally induced structural transformation in the solid state of 2 into 1 occurred upon further heating despite the fact that such a transformation involves major rearrangement of the whole structure. The transformation of the mononuclear complex 3ROH into polymer 1 in the solid-state could be explained by movement of neighboring molecules which are orientated favorably. The thermal loss of ROH molecules and interconnection of mononuclear species appear to take place in a single step. The exclusive formation of the polymer in the solid state is consistent with the preference for the formation of the polymer at high concentrations of building units. ’ ASSOCIATED CONTENT
bS
Supporting Information. (1) Scheme for ligand, (2) analytical and spectral data, (3) experimental procedure for 3DMSO, (4) X-ray powder diffraction patterns, (5) DSC and TG curves, (6) figures for compounds. This information is available free of charge via the Internet at http://pubs.acs.org/. Crystallographic data sets for the structures 1, 2 (at 120 K), 2 (at 295 K), 3EtOH, and 3PrOH are available through the Cambridge Structural Database with deposition nos. 798565798569, respectively. Copies of this information may be obtained free of charge from the director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (fax: þ44 1223 336 033; e-mail:
[email protected] or http://www.ccdc.cam.ac.uk).
’ AUTHOR INFORMATION Corresponding Author
*Tel: þþ385-1-4606353. Fax: þþ 385-1-4606341. E-mail:
[email protected].
’ ACKNOWLEDGMENT Financial support for this research was provided by Ministry of Science and Technology of the Republic of Croatia (Grant Nos. 119-1191342-1082 and 119-1193079-1084).
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